[Fungi]

You’re not gonna’ like this, but if it is dark, how can it be seen? And if you cannot see it, how can you make an experiment to prove it exists when none of it has been found? Just a question, don’t think too hard SC.

[who_would_fardels_bear]

We can't "see" gravity, but we can see and measure its effects.

That is what these scientists are doing with regard to Dark Matter.

Similarly, we can't see Hillary's deleted emails, but they seem to be having a negative effect on her candidacy.

[Cboldt]

Picture how the solar system bodies orbit the sun. Outer planets take longer to make an orbit than inner planets. That same sort of action ought to take place as stars orbit the center of mass of their galaxies. But galaxies don't behave that way, they more or less rotate as a unit. If the solar system did that, a Jupiter year would be about the same as an Earth year, and in turn about the same as a Mercury Year. Dark matter has been proposed to explain the "orbit" observations, of stars relative to their galaxies.

Not saying that proves dark matter exists, but I haven't heard of an alternative mechanism to explain the observations.

[ETL]

if it is dark, how can it be seen? And if you cannot see it, how can you make an experiment to prove it exists when none of it has been found?

They can detect it by its gravitational effects on other objects, such as galaxies. According to standard physics, the further stars are from the center of their host galaxy, the slower they are supposed to orbit. However, observations show that these outer stars orbit at faster than expected rates. Therefore theorists conclude that some mysterious force must be at work. A good candidate is gravity exerted by an invisible source. ie, "dark matter"